1. Field of the Invention
The field of the invention relates to polyamideimide polymers prepared from N,N'-diacylated aliphatic, cycloaliphatic or araliphatic diamines, tricarboxylic acid anhydride compounds and aliphatic, cycloaliphatic or araliphatic diamines and to molded objects and fibers prepared from these polymers.
2. Background
Injection moldable amide-imide polymers have been prepared utilizing aromatic diamines. This is disclosed in U.S. Pat. Nos. 4,016,140 (1977) and 3,573,260 (1971). The prior art does not disclose that injection molded, melt prepared, crystalline objects can be prepared from aliphatic diamine moieties. Except for the aforerecited patents, the prior art discloses that the major application of amide-imide polymers has been as wire enamels. This is illustrated in U.S. Pat. Nos. 3,817,942 (1974), 3,661,832 (1972), 3,454,890 (1970) and 3,347,878 (1967). British Specification No. 570,858 (1945) discloses the general state of the art.
The general object of this invention is to provide melt prepared, ordered, linear, crystalline injection moldable polymers containing aliphatic, cycloaliphatic and araliphatic moieties. A more specific object of this invention is to provide polyamide-imide polymers containing aliphatic amine moieties which polymers are suitable for use as an engineering plastic particularly for use in injection molding and the manufacture of fibers. Another object is to provide suitable nucleating agents for the polyamide-imide polymers to enhance the crystallization rate of the ordered polyamide-imide polymers.
We have now found that injection moldable polyamide-imide polymers can be produced by reacting diacylated aliphatic, cycloaliphatic and araliphatic diamines with tricarboxylic acid anhydride compounds and aliphatic diamines, cycloaliphatic and araliphatic diamines in a molar ratio of about 1.2:2:0.8 to 0.8:2:1.2, advantageously in a molar ratio of about 0.9:2:1.1 to about 1.1:2:0.9 at a temperature of about 100.degree. to 700.degree. F. to obtain an injection moldable amide-imide polymer. The order for the addition of the reactants is not critical and all reactants can be added simultaneously or in any order desired. It has been discovered that the acylated diamine reacts preferentially with the acid groups of the tricarboxylic acid anhydride compound and that all the reatants, acylated aliphatic diamine, tricarboxylic anhydride compound and aliphatic diamine can be combined in the presence of the organic polar solvent such as dimethyl acetamide. Furthermore, acylated diamine need not be isolated or purified prior to its combination with the tricarboxylic acid anhydride compound and the aliphatic diamine.
The injection moldable linear polyamide-imide polymer of this invention comprises the following repeating structural unit ##STR1##
In the foregoing structural unit Z is a trivalent aromatic radical. Z may be a trivalent radical of benzene, naphthalene, biphenyl, diphenyl ether, diphenyl sulfide, diphenyl sulfone, ditolyl ether, and the like.
Useful aromatic tricarboxylic acid anhydrides which contribute the trivalent radical moiety of Z include those compounds containing at least one pair of carboxyl groups in the ortho position with respect to each other or otherwise situated in a fashion which permits the formation of an anhydride structure, one other carboxyl group and from 9 to 21 carbon atoms. Within these limits, these compounds may contain one or more benzenoid rings such as, for instance, trimetallic anhydride and its isomers and multiring compounds such as the 1,8-anhydride of 1,3,8-tricarboxylnaphthalene. Usually these compounds contain up to three benzenoid rings.
The aromatic tricarboxylic acid anhydride used in the novel process to form the polyamide-imide polymers of this invention is of the formula: ##STR2## where Z is a trivalent aromatic radical defined as set forth hereinabove. The following aromatic tricarboxylic anhydrides are preferred: trimellitic acid anhydride; 2,3,6-naphthalene tricarboxylic anhydride; 1,5,6-naphthalene tricarboxylic anhydride, and the like; 2,6-dichloronaphthalene-4,5,7-tricarboxylic anhydride, and the like. One of the preferred aromatic tricarboxylic anhydrides is trimellitic anhydride since this compound is readily available and forms polymers having excellent physical properties of tensile strength and elongation and is resistant to high temperatures.
R and R.sub.1 may be the same or be different and are divalent araliphatic, aliphatic, or cycloaliphatic radicals of from 2 to 18 carbon atoms in which carbon atoms attached to N are aliphatic carbon atoms and R.sub.2 is an aliphatic radical of from 1 to 5 carbon atoms. R and R.sub.1 are derived from aliphatic diamines such as ethylenediamine, tetramethylenediamine, hexamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 4,4'-diamino(dicyclohexylmethane), xylylenediamine. The preferred diamines include 1,6-diaminohexane, 1,2-diaminoethane, 1,8-diaminooctane, 1,12-diaminododecane, 1,10-diaminodecane, 1,4-diaminobutane.
Low molecular weight polyamide-imides from aliphatic diamines have been prepared by a variety of methods by the prior art. However, none of these methods have produced polymers which are useful for injection molding applications. Applicants have discovered a process for the preparation of ordered linear crystalline injection moldable amide-imide polymers, which process comprises reacting fully acylated aliphatic, cycloaliphatic or araliphatic diamines with tricarboxylic acid anhydride compounds and aliphatic, cycloaliphatic or araliphatic diamines in a molar ratio of about 1:2:1 at a temperature of about 100.degree. to 700.degree. F., preferably 150.degree. to 650.degree. F. Optionally the polymer may be further polymerized under solid state polymerization conditions at a temperature of about 400.degree. to 550.degree. F. The resulting high molecular weight injection moldable polymer obtained has an inherent viscosity in the range of 0.4 to 3.0. For the purpose of this invention inherent viscosity is measured at 25.degree. C. and 0.5% w/v in 60/40 w/w/ phenol/1,1,2,2-tetrachloroethane. The term "solid state polymerization" refers to chain extension of polymer particles under conditions where the polymer particles retain their solid form and do not become a fluid mass. These polymers have excellent mechanical and thermal properties and can be readily injection molded. This injection moldability of these polymers can be partially attributed to the fact that these polymers are linear and are not cross linked. Injection molding of the polymers is accomplished by injecting the polymer into the mold maintained at a temperature of about 100.degree.-500.degree. F. In this process a 0.1-2.0 minutes cycle is used with a barrel temperature of about 400.degree. F. to 700.degree. F. The injection molding conditions are given in Table I.
TABLE I ______________________________________ Mold Temperature 100-500.degree. F. Injection Pressure 2,000-20,000 psi and held for 0.2-15.0 seconds Back Pressure 0-400 psi Cycle Time 5-120 seconds Extruder: Nozzle Temperature 400.degree. F. to 700 .degree. F. Barrel Temperature 400.degree. F. to 700.degree. F. Screw: 10-200 revolutions/minute ______________________________________
These injection molding polymers can also be filled from about 20 to 60 weight percent with glass fibers, glass beads, mineral fillers, or mixtures thereof. Suitably, the aforementioned molding compositions may contain from about 30 to 50 weight percent of glass fibers, glass beads, mineral fillers, or mixtures thereof.
The mechanical properties of the polymers prepared in the Examples are given in Tables III through VI and Table VIII.
The solid state polymerization is carried out below the melting point of the polymer and can be conducted in several ways. However, all the techniques require heating the ground or pelletized polymer below the polymer melting point, generally of about 400.degree. to 550.degree. F. while either sparging with an inert gas, such as nitrogen, or operating under vacuum. In applicants' process the acylated diamine need not be isolated or purified prior to its further reaction with the tricarboxylic acid anhydride compound and the aliphatic diamine. Therefore, one can react two moles of acetic anhydride or propionic anhydride and one mole of the aliphatic diamine and use the resulting diacylated diamine solution in acetic acid or propionic acid to react the two moles of tricarboxylic anhydride compound and one mole of diamine and heat the mixture to complete imidization without purification or isolation. Diacylating agents for the diamines include acetic anhydride or acid, or propionic acid or anhydride or any aliphatic acid or anhydride containing from 2 to 8 carbon atoms per acid, preferably 2 to 4 carbon atoms per acid or 4 to 16 carbon atoms per anhydride, preferably 4 to 8 carbon atoms. Formic acid cannot be used as an acylating agent in this process. Usually, high molecular weight crystalline polyamide-imide polymers result.
It should be noted that prior to full imidization in our process there is an intermediate polyamic acid formed of the following structure: ##STR3## which upon further heat treatment converts to ##STR4## and then to the injection moldable final polyamide-imide polymer disclosed hereinbefore. The values for Z and R are the same as used throughout this specification.
It has been found that to facilitate the injection moldability of the polymer produced according to applicants' novel process, nucleating agents may be employed. Without using a nucleating agent, crystalline, fiberglass reinforced samples can be obtained by injection molding if the mold temperature is maintained at a level of about 300.degree. to 400.degree. F. and the mold remaines closed during the long crystallization part of the cycle. However, the rate of crystallization of the polymer may be so slow that the cycle time on occasion could be uneconomical. To obviate this problem, applicants have discovered effective nucleating agents. The more effective of these agents has been talc when used in about 0.01 to 10.0 weight % of the total polymer, preferably about 0.05 to 4.0 weight %. For example, it has been found that fumed silicas and zinc oxide show no effect and are useless as nucleating agents. When talc was utilized, the crystallization temperature of the polymer increased from 199.degree. to 223.degree. C. The use of talc as a nucleating agent lowers the induction period for the onset of crystallization of about 10 fold and also lowers the half-life from about 90 seconds to 30 seconds at 200.degree. C.
The following examples illustrate the preferred embodiments of this invention. It will be understood that these examples are for illustrative purposes only and do not purport to be wholly definitive with respect to the conditions or scope of the invention.
Examples 1 through 9 illustrate our invention and demonstrate that as the ratio of diacetyldiamine: trimellitic anhydride: diamine approach 1:2:1, the rates of crystallization of the polymer and the heat deflection temperatures at 264 psi of the molded, glass reinforced specimens, attain their highest values. In general, as the rate of crystallization becomes faster, the injection molding cycle will also become faster and more economical. Furthermore, as the heat deflection temperature of a molded polymer increases, the maximum temperature at which the polymer can be used will also increase. Both of these valuable features are necessary to make useful injection moldable objects utilizing less expensive acylated and unacylated aliphatic diamines. The other examples illustrate the acetylation of the diamine, further polymer preparation, solid state polymerization, and use of nucleating agents.